Elastic-plastic analysis of pressure vessels and rotating disks made of functionally graded materials using the isogeometric approach

An NURBS-based isogeometric analysis for elastic-plastic stress in a cylindrical pressure vessel is presented. The vessel is made of a ceramic/metal functionally graded material, i.e. a particle-reinforced composite. It is assumed that the material plastic deformation follows an isotropic strain-hardening rule based on the von Mises yield criterion. The mechanical properties of the graded material are modelled by the modified rule of mixtures. Selected finite element results are also presented to establish the supporting evidence for validation of the isogeometric analysis. Similar analyses are performed and solutions for spherical pressure vessel and rotating disk made of FGMs are also provided

Decomposition of 1,1-Dichloroethane and 1,1-Dichloroethene in an electron beam generated plasma reactor

An electron beam generated plasma reactor is used to decompose low concentrations (100–3000 ppm) of 1,1-dichloroethane and 1,1-dichloroethene in atmospheric pressure air streams. The energy requirements for 90% and 99% decomposition of each compound are reported as a function of inlet concentration. Dichloroethene decomposition is enhanced by a chlorine radical propagated chain reaction. The chain length of the dichloroethene reaction is estimated to increase with dichloroethene concentration from 10 at 100 ppm initial dichloroethene concentration to 30 at 3000 ppm. Both the dichloroethane and dichloroethene reactions seem to be inhibited by electron scavenging decomposition products. A simple analytic expression is proposed for fitting decomposition data where inhibition effects are important and simple first order kinetics are not observed

Analytical, experimental and numerical study of a graded honeycomb structure under in-plane impact load with low velocity

Given the significance of energy absorption in various industries, light shock absorbers such as honeycomb structure under in-plane and out-of-plane loads have been in the core of attention. The purpose of this research is the analyses of graded honeycomb structure (GHS) behaviour under in-plane impact loading and its optimisation. Primarily, analytical equations for plateau stress and specific energy are represented, taking power hardening model (PHM) and elastic–perfectly plastic model (EPPM) into consideration. For the validation and comparison of acquired analytical equations, the energy absorption of a GHS made of five different aluminium grades is simulated in ABAQUS/CAE. In order to validate the numerical simulation method in ABAQUS, an experimental test has been conducted as the falling a weight with low velocity on a GHS. Numerical results retain an acceptable accordance with experimental ones with a 5.4% occurred error of reaction force. For a structure with a specific kinetic energy, the stress–strain diagram is achieved and compared with the analytical equations obtained. The maximum difference between the numerical and analytical plateau stresses for PHM is 10.58%. However, this value has been measured to be 38.78% for EPPM. In addition, the numerical value of absorbed energy is compared to that of analytical method for two material models. The maximum difference between the numerical and analytical absorbed energies for PHM model is 6.4%, while it retains the value of 48.08% for EPPM. Based on the conducted comparisons, the numerical and analytical results based on PHM are more congruent than EPPM results. Applying sequential quadratic programming method and genetic algorithm, the ratio of structure mass to the absorbed energy is minimised. According to the optimisation results, the structure capacity of absorbing energy increases by 18% compared to the primary model

Direct determination of turbulent burning velocity during aluminum flame propagation: A comparison of three experimental methods

Burning velocity is a key parameter of main flame propagation models. However, its experimental determination while studying propagating dust flame is still challenging. In this work, aluminum flame propagation in a vertical tube is studied. Two aluminum powders with median diameters of 6.2 and 20.7 μm are analyzed for different equivalence ratios with air. The main objective of this work is to compare the methods commonly used in the literature to determine the burning velocity in the case of propagating flames. One of these methods is based on the estimation of the thermal expansion coefficient. This article focuses first on the estimation of this coefficient and presents the limits of considering the adiabatic flame temperature for its estimation. As detailed in the paper, these methods have some limitations and are therefore compared with an innovative method based on a local direct determination of the burning velocity. This local method is based on the measurement of the unburned flow velocity just ahead of the propagating flame front by Time-Resolved Particle Image Velocimetry (TR-PIV). The methods commonly used in the literature mainly underestimate the burning velocity when compared with the local method. The local method is then used to study the influence of the particle size distribution and the equivalence ratio on the turbulent burning velocity. Firstly, we observe that the turbulent burning velocity increases while the flame is propagating in the vertical tube. Furthermore, the turbulent burning velocity with the 6-μm powder is higher than with the 20-μm powder

Osteoprotegerin in juvenile rheumatoid arthritis: cross talk between the immune and the skeletal systems

Background: Previous studies have linked the decreased local production of osteoprotegerin (OPG), an osteoclastogenesis blocking agent, in the inflamed joints of rheumatoid arthritis patients to the development of bone erosion. Objective: We sought to assess OPG expression in juvenile rheumatoid arthritis (JRA) and to determine its relation to clinical and laboratory markers of disease activity, and radiologic evidence of bone resorption, as well as its relation to the type of onset, duration of illness and different therapeutic modalities. Methods: The study included 40 children and adolescents with JRA, as well as, 20 clinically healthy age- and sex- matched subjects for comparison. The patients underwent clinical evaluation for disease activity by the summed joint index and investigations including assessment of ESR, CRP, antinuclear antibodies and rheumatoid factor. were Serum levels of osteoprotegerin were assayed by ELISA in the patient and control groups. Joints were evaluated radiologically using the modified Larsen index (LI). Results: The serum levels of OPG in the patients [ median (interquartile range): 0.474 (0.4) ng/ml] were comparable to those of the control group [0.495 (0.41) ng/ml] (p=0.29). However, patients with pauciarticular onset JRA had significantly lower OPG levels [0.3 (0.23) ng/ml] than the control group (p= 0.007). The OPG levels were below the 5th percentile of the control value in 60% of pauciarticular and 16.7% of polyarticular JRA cases. Patients with polyarticular JRA had significantly higher values of ESR, activity score and Larsen indices as well as serum OPG levels (p= 0.001, 0.001, 0.002 and 0.02, respectively). OPG levels did not correlate to the ESR or the activity score index values. On the other hand, the duration of illness showed a tendency to be negatively correlated to serum OPG (r= -0.309, p=0.05). LI correlated positively to the activity score index and to the ESR in the JRA patients, whether compiled in one group or classified into subgroups according to disease onset. However, OPG was not significantly correlated to the LI (r= 0.023). The different modalities of therapy did not seem to influence the serum levels of OPG (χ2 = 4.21). Conclusion: Serum OPG expression was low in JRA, especially in the pauciarticular variety. OPG levels were higher in polyarticular JRA, but this does not necessarily have a protective effect since the proinflammatory process is known to promote also the expression of RANKL, an osteoclastogenesis enhancer. While clinical and biochemical parameters of activity, and LI did not correlate to OPG, the latter seemed to be adversely affected by increased disease duration.Keywords: Osteoprotegerin, JRA, osteoclastogenesis, RANKL, bone resorptionEgypt J Pediatr Allergy Immunol 2004; 2(1): 38-4